fix: video size error handling — validation, timeouts, failure surfacing

Backend:
- Increase ffmpeg/ffprobe timeouts from 15s to 60s for large videos
- Classify processing errors (timeout, OOM, corrupt) with user-facing messages
- Emit failure details via media:job:update socket event (error field)
- Bump refboard container memory 512M → 1G

Frontend:
- Client-side file size validation (200MB) before upload starts
- Oversized files show immediate error in upload manager, skip upload
- Handle media:job:update status='failed' — surface error in upload panel
- Add processingFailed() to UploadManager for video processing errors

backend/services/media-worker.js

@@ -85,14 +85,14 @@ async function processJob(job) {
     const image = getImage(imageId);
     if (!image) {
       updateMediaJob(jobId, { status: 'failed', error: 'Image record not found' });
-      emitJobUpdate(boardId, jobId, imageId, 'failed');
+      emitJobFailed(boardId, jobId, imageId, 'Image record not found');
       return;
     }
 
     const videoBuffer = await fetchFromMinio(image.minio_path);
     if (!videoBuffer) {
       updateMediaJob(jobId, { status: 'failed', error: 'Failed to fetch video from storage' });
-      emitJobUpdate(boardId, jobId, imageId, 'failed');
+      emitJobFailed(boardId, jobId, imageId, 'Failed to fetch video from storage');
       return;
     }
 
@@ -131,13 +131,23 @@ async function processJob(job) {
   } catch (err) {
     console.error('[media-worker] Job %s failed:', jobId, err.message);
 
+    // Classify error for user-facing message
+    let userError = 'Video processing failed';
+    if (err.killed || err.signal === 'SIGTERM') {
+      userError = 'Video processing timed out — file may be too large or corrupt';
+    } else if (err.message?.includes('ENOMEM') || err.message?.includes('Cannot allocate')) {
+      userError = 'Out of memory — video file is too large to process';
+    } else if (err.message?.includes('Invalid data')) {
+      userError = 'Invalid or corrupt video file';
+    }
+
     const attempts = (job.attempts || 0) + 1;
     if (attempts < 3) {
       updateMediaJob(jobId, { status: 'retry', attempts, error: err.message });
       emitJobUpdate(boardId, jobId, imageId, 'retry');
     } else {
       updateMediaJob(jobId, { status: 'failed', attempts, error: err.message });
-      emitJobUpdate(boardId, jobId, imageId, 'failed');
+      emitJobFailed(boardId, jobId, imageId, userError);
     }
   }
 }
@@ -173,4 +183,11 @@ function emitJobUpdate(boardId, jobId, imageId, status, result) {
   });
 }
 
+/**
+ * Emit a job failure with error details to the board room.
+ */
+function emitJobFailed(boardId, jobId, imageId, error) {
+  emitJobUpdate(boardId, jobId, imageId, 'failed', { error });
+}
+
 module.exports = { startMediaWorker, stopMediaWorker };

backend/video-utils.js

@@ -34,7 +34,7 @@ function probeVideo(buffer) {
       '-show_format',
       '-show_streams',
       tmpFile,
-    ], { timeout: 15000 }, (err, stdout) => {
+    ], { timeout: 60000 }, (err, stdout) => {
       cleanup(tmpFile, tmpDir);
       if (err) {
         console.warn('[video-utils] ffprobe failed:', err.message);
@@ -91,7 +91,7 @@ function extractPoster(buffer) {
       '-q:v', '3',           // JPEG quality (2=best, 31=worst)
       '-y',                  // overwrite
       tmpOutput,
-    ], { timeout: 15000 }, (err) => {
+    ], { timeout: 60000 }, (err) => {
       if (err) {
         console.warn('[video-utils] ffmpeg poster extraction failed:', err.message);
         cleanup(tmpInput, tmpDir);